[英]plm with time effects
I'm trying to use the plm package in R for the first time. 我正在尝试第一次在R中使用plm软件包。
I wish to estimate a pooling model with only time dummies, ie no unobserved heterogeneity. 我希望估计一个只有时间虚拟的池模型,即没有未观察到的异质性。
I run a simple simple regression of the form: 我运行以下形式的简单回归:
plm(dep ~ x:y -1, data=data, index=c("panel_var", "time_var"), effect="time", model="pooling")
, where x is a continuous and ya categorical variable (and hence x:y the interaction). ,其中x是连续的ya类别变量(因此x:y是交互作用)。 I added
-1
to the model to not include an intercept given that I wished to have time dummies. 考虑到我希望有时间假人,我在模型中添加了
-1
,以不包括截距。
When using summary
, the model correctly informs me time size of the 'panel' and 'time' dimensions. 使用
summary
,模型会正确告知我“面板”和“时间”尺寸的时间大小。 However, it does not report the time dummies. 但是,它不报告虚拟时间。 By inspection I found out that it is because it does not include time dummies in the regression (running a simple
lm
regression without an intercept gives the same answer). 通过检查,我发现这是因为它在回归中不包括时间虚拟变量(运行没有截距的简单
lm
回归给出相同的答案)。
Given that effect="time"
option does not add time dummies, what does it do? 鉴于
effect="time"
选项不会添加时间虚拟变量,它有什么作用?
I know that my desired model can be run with lm
but I wanted to explicitly state the panel structure and use the vcovSCC
covariance structure included in the plm package (although this is probably feasible also after running an lm
regression). 我知道我想要的模型可以与
lm
一起运行,但是我想明确声明面板结构并使用plm包中包含的vcovSCC
协方差结构(尽管在运行lm
回归后这可能也是可行的)。
Thanks for help! 感谢帮助!
A pooled OLS model has neither time nor individual effects. 汇总的OLS模型既没有时间也没有个人影响。 Maybe the package should issue an error message.
也许程序包应该发出错误消息。 You probably want a fixed effects model, eg
您可能需要固定效果模型,例如
data(Grunfeld, package="plm")
# estimate model with time effects
fe <- plm(inv ~ value + capital, data=Grunfeld, model = "within", effect = "time")
summary(fe)
# extract time effects
fixef(fe)
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